Human factors testing of a prototype head movement monitoring system was completed during this reporting period. This device measures head position in Euler coordinates continuously during positron emission tomography (PET) of the brain. These position data will then be used to correct any errors in the brain images produced by head movement during the scan. This correction technique should reduce the magnitude of motion artifacts introduced by head movement, thereby improving quality and quantitative accuracy of PET brain images. Previously developed methods for reducing the deleterious effects of scattered radiation on single photon emission computed tomography (SPECT) images were evaluated using data acquired with a specially modified gamma camera that is able to acquire energy spectra at every image point. Simultaneously, computer simulation studies were undertaken to validate attenuation correction methods which would be used in conjunction with scatter correction. Procurement of a scanning attenuation source was initiated so that scatter and attenuation methods together can be experimentally evaluated in complex objects. Preliminary results suggest that these correction methods will substantially improve the quantitative accuracy of SPECT images of body organs.